Remove some dead code from rendering/ folder

Source/core/rendering/RenderIFrame.cpp

Index: Source/core/rendering/RenderIFrame.cpp
diff --git a/Source/core/rendering/RenderIFrame.cpp b/Source/core/rendering/RenderIFrame.cpp
index 53c03055a5f205d44b9a44da854e7b5dbc5b43a1..d39f30575b46866253d40fdded524c2078490de0 100644
--- a/Source/core/rendering/RenderIFrame.cpp
+++ b/Source/core/rendering/RenderIFrame.cpp
@@ -63,14 +63,6 @@ LayerType RenderIFrame::layerTypeRequired() const
     return ForcedLayer;
 }
 
-RenderView* RenderIFrame::contentRootRenderer() const
-{
-    // FIXME: Is this always a valid cast? What about plugins?
-    ASSERT(!widget() || widget()->isFrameView());
-    FrameView* childFrameView = toFrameView(widget());
-    return childFrameView ? childFrameView->frame().contentRenderer() : 0;
-}
-
 void RenderIFrame::layout()
 {
     ASSERT(needsLayout());